During the combustion process in an IC engine (e.g., a diesel-powered engine), sulfur is concurrently formed with carbon monoxide (CO) and hydrocarbons (HC) as various sulfur oxides (SOx). Typically, 97-99% of the total amount of SOx present in exhaust gas includes sulfur dioxide (SO2) and 1-3% includes sulfur trioxide (SO3). Thus, fuels with higher sulfur content tend to produce higher amounts of SO3. For example, fuel with sulfur content of 1000 ppm may form approximately 1-3 ppm SO3.
Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) catalyst to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3). Generally in such conventional aftertreatment systems, an exhaust reductant, (e.g., a diesel exhaust fluid such as urea) is injected into the aftertreatment system to provide a source of ammonia, and mixed with the exhaust gas to partially reduce the SOx and/or the NOx gases. The reduction byproducts of the exhaust gas are then fluidically communicated to the catalyst included in the SCR aftertreatment system to decompose substantially all of the SOx and NOx gases into relatively harmless byproducts which are expelled out of such conventional SCR aftertreatment systems.
SO3 can react with ammonia to produce ammonium sulfate ((NH4)2SO4) and ammonium bisulfate (NH4HSO4). In conventional selective catalytic reduction systems for aftertreatment of exhaust gas (e.g., diesel exhaust gas) urea is often used as a source of ammonia for reducing SOx and NOx gases included in the exhaust gas of IC engines (e.g., diesel exhaust gas). The urea or any other source of ammonia communicated into conventional aftertreatment systems can be deposited on sidewalls and/or components of the aftertreatment system. Furthermore, the efficiency of the aftertreatment system can depend on the mixing of the exhaust reductant with the exhaust gas, the temperature of the exhaust gas, and/or the backpressure experienced by the exhaust gas.